A swashplate type variable-capacity compressor used for an automobile air-conditioning system, etc., comprises, for example, a rotational axis driven by the rotational force of an engine to turn; a swashplate connected to the rotational axis in a manner allowing for change in its inclination angle relative to the rotational axis; and a compression piston connected to the swashplate, wherein the inclination angle of the swashplate is changed to change the stroke of the piston and thereby control the discharge rate of refrigerant gas.
This inclination angle of the swashplate is continuously changed by utilizing the intake pressure in an intake chamber that takes in refrigerant gas, the discharge pressure in a discharge chamber that discharges refrigerant gas pressurized by the piston, and the control chamber pressure in a control chamber (crank chamber) that houses the swashplate, while also using a capacity control valve driven by electromagnetic force to open/close in order to control the pressure in the control chamber as deemed appropriate, thereby adjusting the balance of pressures acting upon both sides of the piston.
For such capacity control valve, one comprising the following, for example, is known, as shown in FIG. 4 (hereinafter referred to as “Prior Art 1”; refer to Patent Literature 1, for example) discharge-side passages 73, 77 communicating a discharge chamber and control chamber; a first valve chamber 82 formed along the discharge-side passages; intake-side passages 71, 72 communicating an intake chamber and the control chamber; a second valve chamber (actuation chamber) 83 formed along the intake-side passages; a valve element 81 where a first valve part 76 positioned in the first valve chamber 82 to open/close the discharge-side passages 73, 77 undergoes reciprocating motion integrally with a second valve part 75 positioned in the second valve chamber 83 to open/close the intake-side passages 71, 72, and the two valve parts open/close in opposite directions; a third valve chamber (capacity chamber) 84 formed along the intake-side passages 71, 72 at a position closer to the control chamber; a pressure-sensitive body (bellows) 78 positioned in the third valve chamber to apply a bias force in the extending (expanding) direction and also to contract as the surrounding pressure increases; a valve seat body (engagement part) 80 provided on the free end of the pressure-sensitive body in the expanding/contracting direction and having a circular seating surface; a third valve part (valve-opening connection part) 79 that moves integrally with the valve element 81 in the third valve chamber 84 and is able to open/close the intake-side passages by engaging with and separating from the valve seat body 80; and a solenoid S that applies an electromagnetic drive force to the valve element 81.
The capacity control valve 70 is also designed in such a way that, if a need arises during capacity control to change the control chamber pressure on the variable-capacity compressor, the discharge chamber and control chamber can be connected to allow for adjustment of the pressure in the control chamber (control chamber pressure) Pc, without having to provide a clutch mechanism on the compressor. Additionally, its constitution is such that, if the control chamber pressure Pc rises while the variable-capacity compressor is stopped, the third valve part (valve-opening connection part) 79 is separated from the valve seat body (engagement part) 80 to open the intake-side passages and thereby communicate the intake chamber and control chamber.
On the capacity control valve 70 thus constituted, the relational expression of the force of each installed spring that generates a snapping force, and the balancing force generated by the pressure of working fluid that flows in, is given by Pc (Ab−Ar1)+Pc (Ar1−As)+Pd (As−Ar2)+Ps (Ar2−Ar1)+Ps×Ar1=Fb+S1−Fsol, based on the constitution shown in FIG. 4. This relational expression can be organized as Pc (Ab−As)+Pd (As−Ar2)+Ps×Ar2=Fb+S1−Fsol.
Then, assuming the relationship of pressure-receiving areas including the effective pressure-receiving area Ab of the pressure-sensitive body (bellows) 78, seal pressure-receiving area As of the first valve part 76, and pressure-receiving area Ar2 of the second valve part 75, to be Ab=As=Ar2, the above expression can be rewritten as Ps×Ar2=Fb+S1−Fsol.
In other words, by making the effective pressure-receiving area Ab of the pressure-sensitive body (bellows) 78, seal pressure-receiving area As of the first valve part 76, and pressure-receiving area Ar2 of the second valve part 75 identical or roughly identical, the control accuracy of the capacity control valve 1 will improve because only the intake pressure Ps flowing from the intake-side passage 71 acts upon the valve element 81.
The symbols in the aforementioned expression are as follows:
Ab - - - Effective pressure-receiving area of the pressure-sensitive body (bellows) 78
Ar1 - - - Pressure-receiving area (cross-section area) of the third valve part 79
As - - - Seal pressure-receiving area of the first valve part 76
Ar2 - - - Pressure-receiving area of the second valve part 75
Fb - - - Snapping (spring) force of the pressure-sensitive body (bellows) (overall)
S1 - - - Spring (snapping) means 85
Fsol - - - Electromagnetic force of the electromagnetic coil
Ps - - - Intake pressure
Pd - - - Discharge pressure
Pc - - - Control pressure (crank chamber pressure)
As described above, to achieve a capacity control valve of good control accuracy, the relationship of pressure-receiving areas including the effective pressure-receiving area Ab of the pressure-sensitive body 78, seal pressure-receiving area As of the first valve part 76, and pressure-receiving area Ar2 of the second valve part 75, must be Ab=As=Ar2, and therefore it can be said that the diameter of the capacity control valve is determined by the diameter of the pressure-sensitive body 78 or diameter of the valve element 81.
In Prior Art 1, the pressure-sensitive body 78 hermetically connects one end of a metal bellows 78A to a partition adjustment part 86 and connects the other end to the valve seat body 80, and a coil spring 87 is housed in the bellows 78A. This bellows 78A is made of phosphor bronze to achieve good workability, but from the viewpoint of spring property, phosphor bronze has a small yield stress as a material itself and cannot ensure a long stroke, and also a bellows made of phosphor bronze tends to undergo characteristic changes such as drop in load when an excessive pressure is applied or during use at high temperature, which makes it impossible to reduce the diameter or eliminate the coil spring 87. To reduce the diameter of a phosphor bronze bellows, the thickness of the bellows must be increased and its length also increased in order to ensure long-enough stroke, meaning that a length dimension greater than the overall length of the current bellows is needed, which could result in poor formability and might also cause the bellows to project from the outer diameter dimension of the compressor because the overall length in the axial direction must be extended. For these reasons, the diameter of the valve element 81 must be increased in order to ensure the “maximum flow rate (valve full-open flow rate)” which is an important characteristic required of a capacity control valve. In other words, producing the bellows 78A using phosphor bronze makes it impossible to ensure a long stroke and therefore necessitates increasing the diameter of the pressure-sensitive body 78 and that of the valve element 81, and also in light of the tendency of such bellows to undergo characteristic changes, the coil spring 87 must be included, and consequently the diameter of the capacity control valve increases.
On the other hand, it is proposed that a control valve of simple structure comprising a pressure-sensitive unit provided in a solenoid unit be obtained by designing the pressure-sensitive unit with a movable end formed on one end of a bellows using strong magnetic material and a fixed end formed on the other end of the bellows using strong magnetic material, and by opposingly positioning the movable end and fixed end inside the bellows with a specified gap provided in between so that the movable end and fixed end form a magnetic circuit for the solenoid unit; wherein such control valve is such that the bellows is formed with stainless material by considering the joining property of the movable end and fixed end formed with strong magnetic material (hereinafter referred to as “Prior Art 2,” refer to Patent Literature 2).
However, the invention of Prior Art 2 was developed with the object of allowing the components of the pressure-sensitive unit to also function as the components of the solenoid unit because the magnetic circuit for the solenoid unit is formed in the pressure-sensitive unit, thereby simplifying the structure and helping reduce the cost, while also making it easy to assemble the control valve, and furthermore the idea of forming the bellows with stainless material is simply a way to achieve good joining property of the movable end and fixed end formed with strong magnetic material and it does not reduce the diameter of the capacity control valve, and consequently the diameter of the capacity control valve, including the outer diameter of the coil, remains large.